The impact of microsomal prostaglandin e synthase 1 on blood pressure is determined by genetic background

Abstract

Prostaglandin (PG)E(2) has multiple actions that may affect blood pressure. It is synthesized from arachidonic acid by the sequential actions of phospholipases, cyclooxygenases, and PGE synthases. Although microsomal PGE synthase (mPGES)1 is the only genetically verified PGE synthase, results of previous studies examining the consequences of mPGES1 deficiency on blood pressure (BP) are conflicting. To determine whether genetic background modifies the impact of mPGES1 on BP, we generated mPGES1(-/-) mice on 2 distinct inbred backgrounds, DBA/1lacJ and 129/SvEv. On the DBA/1 background, baseline BP was similar between wild-type (WT) and mPGES1(-/-) mice. By contrast, on the 129 background, baseline BPs were significantly higher in mPGES1(-/-) animals than WT controls. During angiotensin II infusion, the DBA/1 mPGES1(-/-) and WT mice developed mild hypertension of similar magnitude, whereas 129-mPGES1(-/-) mice developed more severe hypertension than WT controls. DBA/1 animals developed only minimal albuminuria in response to angiotensin II infusion. By contrast, WT 129 mice had significantly higher levels of albumin excretion than WT DBA/1 and the extent of albuminuria was further augmented in 129 mPGES1(-/-) animals. In WT mice of both strains, the increase in urinary excretion of PGE(2) with angiotensin II was attenuated in mPGES1(-/-) animals. Urinary excretion of thromboxane was unaffected by angiotensin II in the DBA/1 lines but increased more than 4-fold in 129 mPGES1(-/-) mice. These data indicate that genetic background significantly modifies the BP response to mPGES1 deficiency. Exaggerated production of thromboxane may contribute to the robust hypertension and albuminuria in 129 mPGES1-deficient mice.

Figure 1

Baseline mean arterial pressure (MAP) in wild-type (black bars, n=8-10) and mPGES1^−/− (white bars, n=5-9) mice on the DBA/1lacJ and 129/SvEv genetic backgrounds. Blood pressure was measured continuously in conscious animals by radiotelemetry. Data are 24-hour mean values for three consecutive days of recordings. *p<0.05 vs. WT, ^# p<0.05 vs. DBA/1lacJ by two-way ANOVA with Bonferroni post test.

Figure 2

Angiotensin II-dependent hypertension in DBA/1lacJ and 129/SvEv mice in the presence and absence of mPGES1. Ang II (1000 ng/kg/min) was infused for three weeks by osmotic mini-pump while blood pressure was measured simultaneously by radiotelemetry. A: Time course of Ang II-induced hypertension in WT and mPGES1-deficient mice on the DBA/1lacJ and 129/SvEv genetic backgrounds. B: Group means for three weeks of Ang II infusion in DBA/1 (WT, n=9; mPGES1^−/−, n=8) and 129/SvEv (WT, n=8; mPGES1^−/−, n=5) mice. *p<0.05 vs. WT, ^# p<0.05 vs. DBA/1 by two-way ANOVA with Bonferroni post test.

Figure 3

Renin mRNA expression in kidneys of DBA/1 and 129/SvEv mice. Whole kidney cDNA was used for real-time quantitative RT-PCR analysis of renin mRNA levels at baseline and after three weeks of Ang II infusion. Data are expressed as % of DBA/1 and 129 WT baseline. * p<0.05 vs. baseline, ^# p<0.05 vs. WT by two-way ANOVA with Bonferroni post test.

Figure 4

Urinary albumin excretion after chronic Ang II infusion in DBA/1 and 129/SvEv WT and mPGES1−/− animals. Albumin levels were measured by ELISA in 24-hour urine samples after three weeks of Ang II infusion. * p<0.05 vs. WT, ^# p<0.05 vs. DBA/1 by two-way ANOVA with Bonferroni post test.

Figure 5

Urinary PGE metabolite excretion. PGE metabolite levels were measured in 24-hour urine samples before and after three weeks of Ang II infusion in DBA/1lacJ (left panel) and 129/SvEv (right panel) mice comparing WT (black circles) and mPGES1-deficient (white circles) mice. * p<0.05 vs. baseline by paired t-test.

Figure 6

Urinary excretion of thromboxane A₂ and prostacylin metabolites. Levels of TxB₂ (top panels) and 6-keto-PGF_1α (bottom panels) were measured in 24-hour urine samples by enzyme immunoassay in DBA/1 and 129 mice. * p<0.05 vs. baseline by paired t-test.

Figure 7

Expression of cyclo-oxygenase (COX) isoforms COX-1 and COX-2 in mouse kidneys. Total RNA was isolated from kidneys and levels of mRNA for COX-1 (upper panels) and COX-2 (lower panels) were measured by real-time RT-PCR at baseline and after three weeks of Ang II infusion in DBA/1 (A,C) and 129/SvEv (B,D) mice. * p<0.05 vs. baseline by two-way ANOVA with Bonferroni post test; ^# p<0.05 vs. WT by two-way ANOVA with Bonferroni post test.